I disagree that they all play the same. They play similarly. Hopefully more differences come into play later on in the development cycle in the game, however some of the differences do actually change how I play the game.
The Iridium for example. They get multiple trade buildings that also increase influence. I find I am far less likely to build up manufacturing when playing them. I tend to focus on influence and money with only a few dedicated planets for manufacturing. I rush build and buy ships and tech from others far more often.
The Altarians do not get the good terriforming techs so I know from the get go that I will need to maximize my planets or they will lose ground at end game.
The Iconians get free upgrades on their starbases so it is faster to swarm starbases with them....
If you are truly not adjusting how you play when you change factions... you are probably missing out on some of the more interesting ways to play.
Personally my favorite faction so far is the Iridium as I much prefer the diplomatic and economic victory over the crushing war victory.